scholarly journals Exocytosis from permeabilized lactating mouse mammary epithelial cells. Stimulation by Ca2+ and phorbol ester, but inhibition of regulated exocytosis by guanosine 5′-[γ-thio]triphosphate

1992 ◽  
Vol 286 (1) ◽  
pp. 13-15 ◽  
Author(s):  
M D Turner ◽  
C J Wilde ◽  
R D Burgoyne
Keyword(s):  
Epithelial Cells ◽  
Protein Secretion ◽  
Phorbol Ester ◽  
Mammary Epithelial Cells ◽  
Post Partum ◽  
Mammary Epithelial ◽  
Independent Manner ◽  
Permeabilized Cells ◽  
A Site ◽  
Golgi Network

Lactating mouse mammary epithelial cells secrete large amounts of milk protein via constitutive or regulated exocytotic pathways. Secretion through both pathways was quantified by assaying the release of [35S]methionine-labelled trichloroacetic acid-precipitable proteins from digitonin-permeabilized secretory acini isolated from mammary glands of 10-day-post-partum lactating mice. Protein secretion from the isolated permeabilized cells was either Ca(2+)-dependent (regulated) or Ca(2+)-independent (constitutive). In both cases there was a requirement for ATP. Addition of the phorbol ester phorbol 12-myristate 13-acetate (PMA) caused a marked increase in the percentage protein secretion from the cells in a Ca(2+)-independent manner. However, the non-hydrolysable GTP analogue guanosine 5′-[gamma-thio]triphosphate (GTP[S]) caused a partial inhibition of Ca(2+)-dependent exocytosis, while having no significant effect on Ca(2+)-independent exocytosis. Thus the GTP[S] is exerting its effect on the regulated pathway at a site subsequent to protein sorting and packaging into secretory vesicles at the trans-Golgi network.

Investigation of the role of microtubules in protein secretion from lactating mouse mammary epithelial cells

1992 ◽  
Vol 102 (2) ◽  
pp. 239-247 ◽  
Author(s):  
M.E. Rennison ◽  
S.E. Handel ◽  
C.J. Wilde ◽  
R.D. Burgoyne
Keyword(s):  
Plasma Membrane ◽  
Epithelial Cells ◽  
Protein Secretion ◽  
Secretory Pathway ◽  
Mammary Epithelial Cells ◽  
Early Stage ◽  
Major Effect ◽  
Vesicle Transport ◽  
Mammary Epithelial ◽  
Mammary Cells

Disruption of microtubules has been shown to reduce protein secretion from lactating mammary epithelial cells. To investigate the involvement of microtubules in the secretory pathway in these cells we have examined the effect of nocodazole on protein secretion from mammary epithelial cells derived from the lactating mouse. Mouse mammary cells have extensive microtubule networks and 85% of their tubulin was in a polymeric form. Treatment with 1 micrograms/ml nocodazole converted most of the tubulin into a soluble form. In a continuous labelling protocol it was found that nocodazole did not interfere with protein synthesis but over a 5 h period secretion was markedly inhibited. To determine whether the inhibition was at the level of early or late stages of the secretory pathway mammary cells were pulse-labelled for 1 h to label protein throughout the secretory pathway before nocodazole treatment. When secretion was subsequently assayed it was found to be slower and only partially inhibited. These findings suggest that the major effect of nocodazole is on an early stage of the secretory pathway and that microtubules normally facilitate vesicle transport to the plasma membrane. An involvement of microtubules in vesicle transport to the plasma membrane is consistent with an observed accumulation of casein vesicles in nocodazole-treated cells. Exocytosis stimulated by the calcium ionophore ionomycin was unaffected by nocodazole treatment. We conclude from these results that the major effect of nocodazole is at an early stage of the secretory pathway, one possible target being casein vesicle biogenesis in the trans-Golgi network.

scholarly journals The α isoform of protein kinase C mediates phorbol ester-induced growth inhibition and p21cip1 induction in HC11 mammary epithelial cells

Oncogene ◽  
1999 ◽  
Vol 18 (48) ◽  
pp. 6658-6666 ◽  
Author(s):  
Eric D Slosberg ◽  
Michael G Klein ◽  
Yao Yao ◽  
Edward Kyu-Ho Han ◽  
Ira Schieren ◽  
...  
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Epithelial Cells ◽  
Growth Inhibition ◽  
Phorbol Ester ◽  
Mammary Epithelial Cells ◽  
Mammary Epithelial ◽  
Kinase C

scholarly journals Proteins are secreted by both constitutive and regulated secretory pathways in lactating mouse mammary epithelial cells

1992 ◽  
Vol 117 (2) ◽  
pp. 269-278 ◽  
Author(s):  
MD Turner ◽  
ME Rennison ◽  
SE Handel ◽  
CJ Wilde ◽  
RD Burgoyne
Keyword(s):  
Epithelial Cells ◽  
Protein Secretion ◽  
Secretory Pathway ◽  
Mammary Epithelial Cells ◽  
Mammary Epithelial ◽  
Dependent Manner ◽  
Cortical Actin ◽  
Isolated Cells ◽  
Pulse Label ◽  
Constitutive Secretion

Lactating mammary epithelial cells secrete high levels of caseins and other milk proteins. The extent to which protein secretion from these cells occurs in a regulated fashion was examined in experiments on secretory acini isolated from the mammary glands of lactating mice at 10 d postpartum. Protein synthesis and secretion were assayed by following the incorporation or release, respectively, of [35S]methionine-labeled TCA-precipitable protein. The isolated cells incorporated [35S]methionine into protein linearly for at least 5 h with no discernible lag period. In contrast, protein secretion was only detectable after a lag of approximately 1 h, consistent with exocytotic secretion of proteins immediately after passage through the secretory pathway and package into secretory vesicles. The extent of protein secretion was unaffected by the phorbol ester PMA, 8-bromo-cAMP, or 8-bromo-cGMP but was doubled by the Ca2+ ionophore ionomycin. In a pulse-label protocol in which proteins were prelabeled for 1 h before a chase period, constitutive secretion was unaffected by depletion of cytosolic Ca2+ but ionomycin was found to give a twofold stimulation of the secretion of presynthesized protein in a Ca(2+)-dependent manner. Ionomycin was still able to stimulate protein secretion after constitutive secretion had terminated. These results suggest that lactating mammary cells possess both a Ca(2+)-independent constitutive pathway and a Ca(2+)-activated regulatory pathway for protein secretion. The same proteins were secreted by both pathways. No ultrastructural evidence for apocrine secretion was seen in response to ionomycin and so it appears that regulated casein release involves exocytosis. Ionomycin was unlikely to be acting by disassembling the cortical actin network since cytochalasin D did not mimic its effects on secretion. The regulated pathway may be controlled by Ca2+ acting at a late step such as exocytotic membrane fusion.

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